Recent developments in the field of compressor design have also been concentrated on undersea arrangements of large compressors which are intended to be used for the pumping of natural gases. Because of the particular operating conditions, in particular because of the greatly restricted accessibility both for maintenance purposes and by means of supply lines, the specialists are confronted with major requirements. The relevant environmental regulations forbid any exchange of substances between the equipment to be installed and the surrounding sea water. Furthermore, sea water is an aggressive medium and extreme pressure and temperature conditions can be found at the various depths in the sea. A further requirement is that the equipment should on the one hand have an extremely long life and on the other hand must be designed to be virtually free of maintenance. An additional exacerbating factor is not-inconsiderable contamination of the medium to be pumped which in some cases is chemically aggressive.
The pumping medium to be compressed, in particular natural gas to be pumped, not only has a frequently varying aggressive chemical composition but is also a carrier of various types of condensation which make compression more difficult, and in particular lead to increased wear of the compressor. For this reason, condensation is separated before the compression process. Even when using very complex separation technology, it is not possible to prevent subsequent deposition of condensation in the compressor unit as well, and this can at least adversely affect the life of a compressor unit. In the case of a compressor unit which is operated under water, there is a further problem in that the lines which supply the pumping medium and carry it away are normally connected only at the operating location and the surrounding medium, for example aggressive seawater, can enter the compressor unit even while it is being transported there, and can lead to damage in the compressor unit.
International patent application WO 92/14062 has already disclosed a pumping station for underwater operation, which also has a compressor which pumps gaseous components from a source of a raw fossil substance from the seabed to land. This document proposes that the rotors of the pumping machines be mounted by means of oil journal bearings, which are lubricated by means of an oil film. The housings of the turbomachines are positioned vertically and, at the lowest point, have a permanently open oil outlet through which other gases and condensation are also dissipated out of the housing. The liquid components from what emerges are pumped to the land, where they are separated. Separate pipelines and a complex processing installation must accordingly be provided. GB 2 226 776 A and WO 95/15428 also disclose an installation such as that in WO 92/14062.